To see into the chamfering methods of the conventional glass sheet chamfering machines, the following method is used in the case where the whole edge of a glass sheet is chamfered as shown in FIGS. 6A and 6B. That is, a glass sheet to be chamfered is secured on a suction table, and then, a value 2000 is inputted into a numeral setting panel of a numeric control counter. Then if a start switch is turned on, the glass sheet on the rotary suction table slowly revolves, and, at the same time, a chamfering wheel motor which has been advanced toward the edge of the glass sheet fast revolves to start chamfering. Then the value of the numeric display panel of the counter is continuously incremented in accordance with the revolutions of the rotary suction table, and, when this value corresponds to the pre-inputted value 2000, a switch is activated by an output signal of the counter, so that the rotary suction table and the chamfering motor should be stopped. Then the chamfering wheel head is withdrawn to be put to a standby position, thereby completing two rounds of crude chamfering. Then, the crude chamfering wheel of the chamfering motor is replaced with a medium crude chamfering wheel, and then, two rounds of medium crude chamfering are carried out. Then the medium crude chamfering wheel is replaced with a fine chamfering wheel, and then, two rounds of fine chamfering are carried out. Then the fine chamfering wheel of the chamfering motor is replaced with a fine grinding wheel, and then, two rounds of fine grinding are carried out, thereby completing the bevel-chamfering of the edge of the glass sheet.
In FIGS. 6A, 6B and 6C, reference code 1 indicates a glass sheet, and la indicates the bevel-chamfered face. Here, the crude chamfering, the medium crude chamfering, the fine chamfering and the fine grinding are carried out respectively twice or more by turning the rotary suction table in accordance with the numeric control of the counter, so that the face of the bevel-chamfering should be sufficiently wide, and that a high chamfering quality should be assured.
Meanwhile, when the curved parts of the edge of a glass sheet is to be chamfered as shown in FIG. 6C, the crude chamfering, the medium crude chamfering, the fine chamfering and the fine grinding are sequentially carried out twice. However, in this case, the chamfering cannot be carried out continuously twice unlike the case where the whole edge is chamfered. In this case, the chamfering is carried out twice discontinuously from the starting point S to the ending point E.
Therefore, the revolution angles between the chamfering starting point S to the chamfering ending point E should be known numerically. For this purpose, a glass sheet is secured on the rotary suction table, and then, a chamfering wheel head 10 is made to advance toward the edge of the glass sheet.
Then, by turning the rotary suction table, the chamfering starting point S is made to be positioned at the middle of two shape sensing rollers 22 which are located below the chamfering wheel 13 as shown in FIG. 7A. Then, a reset button of the counter is pressed to clear the value of the numeric panel to "0000". Under this condition, the operator grasps an adjusting key handle 25b of a chamfering direction indicating device, and one of the two shape sensing rollers 22 is made not to revolve in the longitudinal direction at the sharp angle of the chamfering starting point of the glass sheet. If one of the two rollers revolves in the longitudinal direction at the starting point S as shown in FIG. 7B, the chamfering head 10 itself automatically revolves, so that the chamfering direction should become wrong so as for the chamfering to be impossible, or that a defective portion 2' is generated as shown in FIG. 7C. Therefore, the operator should make sure that the two glass sheet shape sensing rollers should be disposed in parallel with the chamfering advancing direction as shown in FIG. 7A by adjusting the adjusting key handle 25b, so that the advancing direction of the chamfering wheel should be parallel with the chamfering advancing direction.
Under this condition, if a switch for forward revolution is turned on, the glass sheet which is secured on the rotary suction table slowly forwardly revolves. Simultaneously, the value of the numeric panel of the counter is incremented starting from "0". When the two glass sheet shape sensing rollers contact with the lateral face as shown in FIG. 7D, the operator releases the adjusting key handle.
From this point, a glass sheet shape sensing device 19 senses the shape of the glass sheet, and the wheel head itself automatically maintains the optimal chamfering direction. The glass sheet continuously revolves, and the value of the counter is continuously incremented. However, when the chamfering ending point comes to be located at the middle of the two sensing rollers, the operator turns off the revolution switch to stop the revolution of the rotary suction table, while holding the adjusting key handle. Then, if the numeric display panel is looked into, there is found a numeric value which is the sum of the revolution angles between the chamfering starting point to the chamfering ending point. This numeric value is inputted into a setting panel of the counter, and then, a reverse switch is turned on, so that the table should revolve reversely. During this procedure, the value of the numeric display panel is decremented until the rotary suction table stops at the value "0", and the chamfering starting point of the glass sheet comes to be positioned at the middle of the two glass sheet shape sensing rollers. At this point also, the operator has to hold the adjusting key handle.
Thus the whole numeric value of the revolution angles are all inputted from the chamfering starting point to the chamfering ending point of the glass sheet to be partially chamfered, thereby making ready for the partial chamfering.
The operator lowers the wheel motor which has been lifted, and turns on the start switch while holding the adjusting key. Then the wheel motor of the wheel head and the rotary suction table revolve, and the chamfering fluid is supplied, thereby starting the partial chamfering. When the two glass sheet shape sensing rollers contact on the lateral face of the chamfering starting point, an automatic chamfering is let to be carried out by releasing the adjusting key. At the same time, the numeric display panel increments its value starting from "0", and when the value on the numeric display panel corresponds with the pre-set value, then an output signal of the counter causes the supply of the cooling fluid to be stopped, and the wheel head to be withdrawn. Also the rotary suction table is rotated reversely, and the numeric display panel shows decrements of its value until it reaches "0" whereupon the rotary suction table is stopped and the system returns to the chamfering starting point.
Again, the operator turns on the advancement switch, while making the chamfering direction of the glass sheet and the chamfering direction of the wheel head be parallel by adjusting the adjusting key. Then the wheel head advances toward the glass sheet, and the operator turns on the start switch while making one of the sensing rollers contact with the lateral face of the chamfering starting point, thereby starting a partial chamfering again. Thus the partial chamfering is carried out, and when the displayed numeric figure corresponds with the pre-set numeric figure, the supply of the cooling fluid is stopped, while the wheel head is withdrawn to be put to a standby position. Then the rotary suction table is rotated reversely to return to the chamfering starting point in an automatic manner.
Thus the two rounds of the crude chamfering is completed, and then, the crude chamfering wheel is replaced with a medium crude chamfering wheel. Then the medium crude chamfering is carried out twice in the above described manner. Then the medium crude wheel is replaced with a fine chamfering wheel, and then, a fine chamfering is carried out twice in the above described manner. Then the fine chamfering wheel is replaced with a fine grinding wheel, and then, a fine grinding is carried out twice in the above described manner.
Thus, when the rotary suction table which secures a glass sheet revolves forwardly (clockwise), the value of the numeric display panel is incremented, while, during its reverse revolution, the numeric value is decremented. As described in Korean Patent Application 91-3090 which was filed by the present applicant, a counter adds or subtracts as much as the pulse signals which are generated in accordance with the revolutions of an encoder which is installed in such a manner as to be rotated together with the shaft of the rotary suction table. Thus the numeric display panel displays numeric value in order to show the revolution angles of the glass sheet of the rotary suction table in a numeric value. The shaft of the rotary suction table and the shaft of the encoder are installed in one to one ratio, and therefore, one revolution of the encoder represents 1000 pulses, while thus one revolution of the rotary suction table represents an angular value of 1000. Further, the machine operates in accordance with the on and off signals of a switch which is installed on the counter, and which is activated when a correspondence between the inputted numeric value and the pre-set numeric value the inputted value is encountered.
Thus, in carrying out a glass sheet edge partial chamfering, the crude chamfering is carried out twice, the medium crude chamfering is carried out twice, the fine chamfering is carried out twice, and the fine grinding is carried out twice. In this procedure, the rotary suction table revolves eight times forwardly and eight time reversely, and the chamfering wheel performs forward advancements eight times and withdrawing eight times, this being a complicated procedure. Further, in this procedure, the adjustments of the adjusting key have to be carried out sixteen times at the chamfering starting point and the chamfering ending point, this being a troublesome task.